It is common in many vehicle applications to use two or more engines, for example in multi-engine boats and airplanes. Multiple engines are most effective when the engine speeds (rpm) are synchronized. If the engines are not synchronized, a noticeable and irritating beat frequency is generated. Operating multiple engines in a non-synchronized mode forces one engine to work harder than the other, which reduces overall efficiency and may lead to premature failure of the vessel structure.
Modern multiple engine boats and aircraft often include expensive synchronization features using various technologies, including, for example, hydraulic power, servo motors, fuel supply control, computerized operation, and drive-by-wire devices.
For obvious safety reasons, synchronization devices require safe failure modes, whereby in the event of failure of the device, the engines remain operable. Further, marine devices must be robust and corrosion resistant to perform reliably in a salt-water environment. A desirable design feature is permits an operator to manually override synchronization, for example when different engine speeds are required for low-speed maneuvers such as docking. This may be achieved, for example, by restricting synchronization to the condition where the engine speeds are within a predetermined range.
As a result of these and other design considerations, the devices of the prior art are generally complex, expensive, bulky, and the cost of installation can be significant due to the requirement for skilled labor and expensive materials. This places most such systems out of the reach of the common boat owner or aircraft owner.
Information relevant to attempts to address these problems can be found, for example, in U.S. Pat. Nos. 5,222,901; 5,142,473; 4,718,869; 5,741,166; 6,414,607; 6,233,943; 6,485,340; 6,587,765; 6,611,748; 6,694,741; 6,751,533; 6,840,888; 6,965,817; 7,121,908; and 7,142,955. However, each one of these references suffers from one or more of the following disadvantages: the devices comprise many parts, increasing the risk of component failure and the cost of manufacture; the devices are of large size, taking up valuable boat or aircraft space; and/or the devices are complex, making installation and maintenance a skilled operation that may be difficult and expensive.
For at least the foregoing reasons, there is a need for a small, low cost, low component count, easily installed and maintained engine synchronizer suitable as original equipment or for retrofitting to multi-engine vehicles such as boats or aircraft, and for OEM applications.